Cheaper? For one, it's not a cheap plastic like Android phones use, and it surrounds a steel frame. Do you know the part costs between the 5 and 5c cases? I doubt it, so you're just full of conjecture.
If I could have gotten one of the 5c colors on my 5s, I would've gone for that. I don't need to justify my expenditures by flashing around a material that "appears" expensive. The 5c is a great design, and let's not forget the 3gs had a plastic back, and I don't remember many people complaining about that. It was also arguably a more durable phone. The aluminum frame is nice, if rather boring, but it scratches and dents fairly easily.
Right. and iPhone 5c is far better built than iPhone 3G ....